Removable flexible coverings are positioned over various members or materials, such as a tarpaulin, sheet, blanket, or the like and it is desired to secure or fasten the covering in a desired position over the member to be covered. The flexible coverings are normally of a generally rectangular shape defining four corners and the present invention is particularly adapted for releasably fastening the corners of such a covering.
One example of such a covering is a sheet on a waterbed. Waterbeds comprising water-filled mattresses are normally supported on a box-like bed frame which includes wooden frame members fastened together at their corners and surrounding the waterbed. It is difficult to retain the sheets on the waterbed in a neat and snug manner on the top of the water filled mattress. While the bed may be made up neatly, the sheets during use begin to become untucked from around the edges of the waterbed mattress. While very large sheets have been utilized heretofore to be tucked under the mattress by providing diagonal straps on the corners of the waterbed sheets, the sheets still become loose from the bed.
Heretofore, various fasteners or securing devices have been utilized for fastening the corners of a sheet over a bed, but such fasteners or devices have not performed in an entirely satisfactory manner. If some "give" is not provided for the member holding the fastener or retainer on the sheet so that the sheet can move, a destructive tearing force may be applied to the sheet or sheeting material. Many prior art devices utilize elastic members for holding a retainer member in place. Elastic materials lose their elasticity over a period of time if a continuous strain or stretch is applied.
For example, U.S. Pat. No. 4,660,240 dated Apr. 28, 1987 and U.S. Pat. No. 4,782,543 dated Nov. 8, 1988 show a device for attaching bed sheets to a waterbed which utilizes a separate unattached button or retainer engaged with a fastener member for applying a sliding force against the sheet wrapped over the button. If any defects occur in the button or sliding fastener, damage to the sheet could result. Additionally, an elastic member is provided to hold the separate button within the fastener. Also, a non-uniform tensional force is applied against the fastener and sheet unless the button is placed exactly in the same location and the sheet is stretched the same amount each time. In usage, the elastic material will increase in length requiring the user to place the button in a different location, but with continued use, the increased length stretch material will apply less and less pull as it permanently stretches out of shape with time. Further, there is a limit to the distance or length that the stretch material can be stretched, and upon reaching this limit, a destructive tearing force may be applied against the sheet by the button.